Heavy Live Load Reduction 2

[JTHandy]

The ICC (2000, 2003) states that if you have a minimum live load of over 100 lbs/sf you can not reduce it, except only for columns (then it is a reduction of 20%). A study guide interprets this to only apply to storage facilities. In an example, they present a library building with a live load of 125 lbs/sf. The example shows that the live load is reduced as appropriate for smaller loads for each of the 5 floors.

When I read the code (1607.9.1.1 or 1607.9.2) there is no mention of storage differentiation. It seems to apply to all live loadings over 100 lbs/sf.

Does anyone have any clarification on this? Am I missing something?

 

[Bagman2524]

Looks to me you have the choice of 2 possible LL reductions.
1607.9.2 is an alternate floor live load reduction.
1607.9.1 is the primary method of determining the LL reduction. If you can satisfy 1607.9.1.1 you can take that reduction.

 

[JAE]

Your study guide, I would say, is in error.

 

[JTHandy]

Is it appropriate to design for 1607.9.1 for all cases? Is 1607.9.2 used as a less conservative backup?

The study guide seems to rely heavily on the latter - does not check the 1607.9.1 spec. I believe the 1607.9.2 is from the UBC. If so, the author is likely providing examples from past experience with the UBC.

 

[Bagman2524]

IBC 1607.9.2 is the same as section 1607.5 of the 1997 UBC. Looks like this was the main method of LL reduction in UBC. It may be that IBC adopted it as an alternative LL reduction method to satisfy the UBC contingent when SBC, BOCA & UBC were originally rolled up in the 1st release of IBC.

Looks to me like IBC 1607.9.1 is applicable for all cases except those listed in 1607.9.1.2, 9.1.3 & 9.1.4.

The primary method of LL reduction in IBC looks very similar to the alternate LL reduction in UBC section 1607.6

SBC-99 section 1604.2 covers LL reduction. It is almost exactly the same as the alternate LL reduction method in Section 1607.9.2 of IBC.

BOCA-99 section 1606.7 covers LL reduction. It is very similar to the primary method of LL reduction in 1607.9.1 of IBC.

After taking a look at all the codes my impression is that the IBC primary method of LL reduction in 1607.9.1 comes from the BOCA LL reduction method and the UBC alternate LL reduction method. The IBC alternate method of LL reduction in 1607.9.2 comes from the UBC and SBC primary LL reduction methods.